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SIP, Presence and Instant Messaging
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
Session Initiation Protocol (SIP)
Developed in mmusic Group in IETF Proposed standard RFC2543, February 1999 Work began 1995 Part of Internet Multimedia Conferencing Suite
Main Functions Invite users to sessions
Find the user’s current location, match with their capabilities and preferencesin order to deliver invitation
Carry opaque session descriptions
Modification of sessions Termination of sessions
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
Protocol Components User Agent Client (UAC)
End systems Send SIP requests
User Agent Server (UAS) Listens for call requests Prompts user or executes program to
determine response
User Agent UAC + UAS
Redirect Server “Network” server; redirects users to try other
server
Proxy Server “Network Server” Proxies request to another
server Can “fork” request to multiple servers, creating a search tree
Registrar receives registrations regarding current user
locations
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Architecture
Request
Response
Media
1
2
3
45
67
8
9
1011
12
SIP Client
SIP Redirect Server
SIP ProxySIP Proxy
SIP Client(User Agent Server)
Location Service
13
14
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Message Syntax Many header fields from
http
Payload contains a media description
SDP - SessionDescription Protocol
INVITE sip:[email protected] SIP/2.0From: J. Rosenberg <sip:[email protected]>Subject: That pay increaseTo: Eric Sumner <sip:[email protected]>Via: SIP/2.0/UDP pc13.dynamicsoft.comCall-ID: [email protected]: application/sdpCSeq: 4711 INVITEContent-Length: 187
v=0o=jdrosen 53655765 2353687637 IN IP4 122.3.44.12s= [email protected]=IN IP4 122.3.44.12t=0 0m=audio 3456 RTP/AVP 0
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Benefits Integration with IP Applications
MIME URIs DNS
Scalability Stateless operation SRV usage Multi-hop networks
Session Independence Usable for interactive games,
chat, voice, video
Recoverability State stored in messages Re-opening of TCP connections
Extension Management Adding headers Adding methods Adding bodies Require and Proxy-Require
Interoperability New Services!
Integration with IM, presence, email, web
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
What Does Presence Have to Do With SIP? How to Deliver Presence
Need a network that can identify users independent of location
Need a way to forward subscription requests to server handling that user
Need a way for user to tell server its location and other presence data
Need a network which can forward notifications to subscribers
Needs to scale Needs to deliver messages in
real time
What Does a SIP Network Do? Identifies users independent of
location Forwards requests (INVITE or
otherwise) to server handling user REGISTER allows network to tell
server its location and other information [later]
Can forward messages back to originators in reverse direction
Scales Delivers messages in real time
(call setup delays)
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Already Provides Publication Capability REGISTER is a Publication Message
for Locations
Allows for SIP and Other URL Types
Multiple Entities Can Publish for the Same Address
SIP Caller Preferences Extension Allows for Attributes for Locations Mobile, landline Home, business Preferences Audio, video - MIME capability
Registrar
Registrar
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Extension for Presence
New Entity: Presence Agent Purely logical entity Knows presence state of user Receives SUBSCRIBE requests Generates NOTIFY requests Co-located with proxy/registrar or User Agent
Basic Operation Subscriber send SUBSCRIBE Routed to PA using normal SIP PA authorizes subscriber Acceptance contains presence state NOTIFY sent when state changes
Routed using SIP Record-Route
REGISTER
SUBSCRIBE
NOTIFY
Presence Agent +Proxy/Registrar = Presence Server
Proxy
Subscriber
Presentity
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
Features of SIP For Presence Extension End Users Can Perform Notifications
Scalability
Presence Agent Function Can Migrate Network provides service when user is offline When user is online, subscriptions migrate to user
Authorization is orthogonal
Multiple Entities Can Generate Presence Information for One Presentity Mobile phone, PDA, laptop and desktop PC
Traditional SIP Proxies Route SUBSCRIBE and NOTIFY
Presence Data is Orthogonal
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
SIP Extension for Instant Messaging Operation of Extension
Messages carried in SIP messages New method - MESSAGE Routed to recipient using normal SIP techniques Simple extension
Features Any MIME data can be sent TCP for large messages Routed by existing proxies and registrars Possible to have a different client for IM and communications
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
Advantages of Using SIP for Presence and IM Unifies Major Communications Services
Voice/video IM Presence
Shared Databases
Shared Proxies
Shared Servers
www.dynamicsoft.comSpring PIM 2001
SIP, Presence and IM
Advantages of Using SIP For Presence and IM Reduces Management Costs
One infrastructure instead of two One NOC instead of two One set of managers instead of two
Enables New Combined Services Combined services integrate voice, video, IM, presence, web amd email These new services will be a “killer app” for communications on
the Internet Delivery of combined services is greatly simplified by alignment of
presence and communication signaling protocols
Information Resource Jonathan [email protected]